Development And Application Of La_0.8Sr_0.2MnO₃/MgAl₂O₄ Wire-mesh Honeycombs For Catalytic Combustion Of Air Diluted Methane

Methane is a strong greenhouse gas with a high combustion heat.Direct discharging of the huge amount ventilation air from coal mine which contains methane below 1 vol.%has not only polluted air but also wasted energy.Highly diluted methane is hard to flame;combustion at high temperatures will generate NOx.Catalytic combustion can reduce greatly the temperature of methane combustion in air,avoid the secondary pollution,and break the limit of methane content.La_1-xSr_xMnO₃ perovskite?LSM?is a cheap catalyst with good activity at medium temperatures for combustion of air diluted methane,once composed with MgAl₂O₄ spinel?MA?support,the activity and sintering resistence of LSM can be improved.Also,the catalytic efficiency can be modified after washcoating the composite powder on the honeycomb substrates made of metallic wire-mesh.In this thesis,the composite powders of LSM and MA in molar ratio of1:n,named as LSM/nMA,were prepared by deposition-precipitation method.The impact of preparation factors,such as the pH of ball-milling process,the molar ratio of Sr in LSM?x?,the molar ratio of support to active phase?n?,and the aging and calcination temperatures of precursors was investigated.The catalytic activity of the powders was examined in the temperature-programmed micro reactor with the 1 vol.%methane in air,and the properties of catalysts were characterized by FTIR,H₂-TPR,BET,XRD and SEM.The LSM/4MA catalyst which precursor aged at 10?and calcined at 800?demonstrated the best activity with T₅₀ as 489.4?and Ea 112.5 kJ/mol,and excellent sintering resistance with SSA of 81.6 m²/g.Afterwards,the wire-mesh honeycomb catalysts were developed by dip-coating sequentially the slurries of MA and LSM/4MA powders on the honeycomb modules?o.d.25 mm?made of surface modified Fe-Cr-Al wire mesh.Influence of MA and LSM/4MA coating was investigated respectively,with 0.5 vol.%methane in air at GHSV of 40000/h,which gave the best amount in preparation of the wire-mesh honeycombs and the proper coating thickness of MA is around 20?m,the best loading of LSM/4MA is about 2.65mg/cm².